Windows 10: PC won't boot to windows after unplugging old hard drive, after setting new SSD with...

Awhile back I installed an SSD into my new machine and brought over the old hard drive to get data off, both have windows 10, now I've upgraded yet again with a new nvme SSD to replace the old hard drive that previously had been the main boot drive since it had games, but when I unplugged it, the PC wouldn't boot, plugging it back in fixes it, but it has nothing in user folder and all the user files were on the older SSD, I googled it and tried using this older fourm https://answers.microsoft.com/en-us/windows/forum/all/how-to-change-bootable-partition/907c92bc-67ff-469c-8cd9-73e86f647de0

:)

 

new ssd, installed win 10, first in boot order but still boots from old hard drive.

I have a pc with a standard hard drive running windows 10 just fine. I got a new SSD. I unplugged all the hard drives, installed the SSD and installed windows 10 on it. I would boot just fine. I then plugged the old hard drive back in thinking I
could switch between these boot drives using the bios boot order. I was able to switch back to booting from the hard drive but now when I change the boot order to the ssd first it always skips over it and boots the from the second option which is the old
hard drive. I thought hard drive data was just data and the bios could choose which drive to boot from but it doesn't. I can see that the old hard drive is listed as active in disk management. It seems like windows will mark only one hard drive as active
and the bios must boot from that no matter what the boot order is. Is that how it works? Is there a way to switch between booting from either drive without opening up the pc and unplugging the other drive each time?

 

new ssd, installed win 10, first in boot order but still boots from old hard drive.

It only shows the os on the previous hard drive and not the one on the ssd. I am confident that if I unplug the other hard drives it will boot from the ssd just fine as it did several times during setup. I did learn that I had to unplug all the other
drives when installing on the ssd as this is the only way the ssd would get the efi and recovery partition that a boot drive seem to need. Disk management also shows the ssd as a "basic data partition", but before I plugged the other hard drives back in it
was listed as a system, boot,.... partition.

It seems that having two windows installations on separate drives and switching between them isn't as simple as doing it with just the bios boot order.

 

Boot from old hard drive

The motherboard of my old computer died suddenly and so I bought a new computer. It has two 1TB HDDs on RAID 0 and comes preinstalled with Windows 10 Home. I wanted my computer to boot from my old 120GB SSD from my old computer but it doesn't seem to recognize it as boot drive. It was working perfectly with my old computer.

I can view files from the SSD and so this confirms that it is working. The boot partition is marked active.

I tried changing the boot hard drive in the bios but in the bios, the only two options shown in the boot menu are

• Windows Boot Manager (Intel Volume1)
  
• CD/DVDRW
  

After searching online, a website suggested swapping the Sata of the old hard drive with that of the new one. I tried even this but this didn't work either. It gave me the error "boot disk not found" and in the boot menu, the only option was "CD/DVDRW".

For Reference :

Motherboard : ASUS Z170 PRO GAMING

All Hard Drives Run GPT.

Any other solutions?